Method of making crucibles



Ecc. 9, 1930. w. R. WHITNEY METHOD OF MAKING CRUGIBLES Filed Nov. 3, 1926 Inventor: Uaul Patented Dec. 9, 1930 UNITED STATES PATl-:Nr` cri-lcs WILLIS R. WHITNEY, 0F NISKAYUNA, NEW YORK, ASSIGNOR .T0v GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK METHOD 0F MAKING cRUcIBLEs .Application` ledNovember 3, 1926. Serial No. 146,047.

My invention relates to Crucibles and more particularly to crucibles for electric induction furnaces, and has for its object the production of a simple and rugged Crucible having a. heating resistor incorporated in its Walls.

My invention has particular application to the making of crucibles used with high frequency electric induction furnaces in which a material having high electrical resistance, such as carbon or graphite, is embedded in the Wall of the crucible to form a heating resistor, electric currents being produc-ed in it by electrical induction.

In carrying out my invention in one form, I construct the crucible from a suitable heat refractory material which may be molded in plastic form, such as fire clay, with which is mixed a suitable. amount of carbon or graphite to form a heatingresistor. After being molded the crucible is suitably fired in a reducing atmosphere and then finally heated in the open air to a temperature sufficient to burnout the carbon or graphite from an outer layer of heat refractory material. This produces a crucible of unitary structure which is provided with an inner embedded heating resistor covered with an outer layer of fire clay forming a lining.

For a more complete understanding of my invention reference should be had to the accompanying drawing in which F ig. l is a view partially in section of a Crucible embodying my invention, while Fig. 2 is a diagrammatic view illustrating the use of the crucible in a high frequency furnace.

Referring to the drawing, the crucible in finished form, as constructed in accordance with my invention, comprises a unitary molded mass of suitable heat refractory material which is provided with an inner portion l0 containing a suitable quantity of high resistance but conductive material suicient to form an electric resistor, this resistor being covered with an outer layer llconsisting of the heat refractory material alone. Ordinarily, crucibles of this type are formed by covering a graphite VCrucible corresponding to the resistor 10 with a layer of heat refractory material.

' In accordance with my invention, the crucible is molded or otherwise formed as a unit. In making the crucible, a suitable amount of high resistanceV material, such as carbon or graphite, is mixed with the plastic heat refractory material, such as fire clay, the resistance material contained being sufficient to give the desired electric resistor heating propertie's. After the crucible has been molded to the desired shape in any suitable manner, it is fired in a reducing atmosphere, for eX-v ample, in a porcelain kiln filled with suitable reducing gas, such as hydrogen. After being fired the crucible is finally heated in the open air so as to burn out the resistance material from an outer layer. This results in an outer layer or lining 1l of lire clay, from which the graphite has been burned, with an inner layer of a mixture of fire clay and graphite forming aresistor. K f

In using the crucible in a high frequency furnace, for example, the Crucible is inserted in a suitable induction coil 12, Fig. 2,'which is supplied with a suitable high frequency Current whereby electric heating currents are induced in the inner resistor 10.

It will be noted that the crucible is very simple in construction, and furthermore very rugged since there is no danger of the lining becoming` loose and detached as often happens When the lining is applied separately.

What I Claim as new and desire to secure by Letters Patent of the United States is l. The method of making a crucible having an inner heating resistor and-an outer heat refractory lining which consists in molding the crucible from a mixture of heat refractory material and powdered resistance heating material, and then burning the resistance heating material out of an outer layer of the heat refractory material so as to leave an inner heating resistor.

2. The method of making a crucible having an inner heat resistor and an outer fire Clay lining which consists in molding the crucible fromthe mixture of lire Clay and graphite and then burning the graphite out of an outer layer of the fire Clay solas to leave an inner heating resistor.

3. The method of making a crucible having an inner heating resistor and an outer heat refractory lining Which consists in molding the Crucible from a mixture of heat refractory material and powderedJ resistance hea-ting material, heating said Crucible ina reducing atmosphere and then heating said Crucible in an atmosphere or air so as to burn the resistance material out of an outer layer of the heat refractory material.

The method of making a Crucible haV- ing an inner heating resistor and an `outer fire Clay lining which Consists in molding the Crucible from a mixture of re Clay and graphite, firing said Crucible in a reducing atmosphere and then heating said Crucible in an atmosphere of air so as to burn the graphite out of the outer layer of the ire clay.

1n Witness whereof, have hereunto set my hand this 2nd day of November, 1926.

WILLIS R. VJHITNEY. 

